The steel ladle is an essential part of steel production as a transport container for liquid steel and for treatment in secondary metallurgy. Furthermore, the steel ladle lining is the largest consumer of refractory products in a steel plant per ton of produced steel. Therefore, minimising refractory consumption is of utmost interest, not only from an economic point of view but extending the ladle lining lifetime can also conserve resources. Currently, lining designs are often based on engineers' experience and empirical rules, which can lead to non-optimal linings. This work aims to understand better the influences of specific geometrical parameters on the thermomechanical behaviour of a steel ladle lining. For this purpose, 2D and 3D simulations of the thermal and thermomechanical behaviour of a slag zone lining are carried out with the Finite-Element software package ABAQUS. The slag zone lining has a three-layer structure and consists of magnesia carbon bricks as wear lining, a high alumina monolithic permanent lining and an insulating layer. The geometrical factors considered are a variation of the initial expansion allowance of the wear lining in the range of 0.2 - 0.8 mm and the variation of the thickness of the insulation layer, from 0 - 12 mm. However, the total lining thickness remains constant and is compensated by the permanent lining. To limit the computational costs, a unit cell approach is applied, and the simulation model is reduced to a quarter of the dimensions of a wear-lining brick, taking advantage of all symmetries. The simulated temperature programme considers the first ladle cycle, including ladle preheating. The Drucker-Prager criterion, the Von Mises creep model and an ABAQUS subroutine developed at the Chair of Ceramics, which combines both material models, are used to model the material behaviour. The results of the variation of the expansion allowance show that with increasing expansion allowance in the circumferential direction, the maximum compressive stresses in the wear lining as well as the maximum tensile stresses in the steel shell are strongly reduced in the circumferential direction. The influence on stresses in the vertical direction is less. The stress reduction due to increasing expansion allowance also leads to decreasing irreversible strains. However, a too high expansion allowance causes open joints during the heat and should be avoided. Based on the 2D thermal simulations performed, a maximum insulation layer thickness of 12 mm was defined for the 3D simulations. A higher insulation layer thickness leads to an increasing temperature difference between the hot side and the steel shell. The 3D simulations show that the insulation layer thickness hardly affects the maximum hot face stresses. The tensile stresses in the steel shell increase significantly with increasing insulation. The joint opening during the idle time until the next heat can be reduced by the higher temperatures in the wear lining.